The injection molding machine is adapted such that, in a state is which the mold is closed by the mold clamping apparatus and a large mold clamping force is being applied to the mold, a high-pressure resin is injected and filled into the cavity of the mold from an injection apparatus, and a resin molding is taken out from the widely opened mold after cooling and solidifying to produce resin moldings of a desired shape. Such a mold clamping apparatus is required to have functions of performing opening and closing operation of the mold in a short time and applying a large mold clamping force to the mold. As one of such mold clamping apparatuses, a toggle type mold clamping apparatus having a toggle link mechanism shown in Patent Document 1 is widely used.
The toggle link mechanism in the toggle type mold clamping apparatus is provided with a plurality of joint portions between a fixed platen and a movable platen. In the bearing bush used in such a joint portion, an equal load is not necessarily applied to the entire circumference of its cylindrical inner peripheral surface, and in an initial stage of mold closing of the movable platen, i.e., in an early period of movement toward mold closing from the open mold state, the speed of the movable platen is fast and the mold closing force is small, so that a large load is not applied to the cylindrical inner peripheral surface of the bearing bush; however, as the completion of mold closing approaches, the speed of the movable platen abruptly decreases, and the mold closing force of the movable platen increases remarkably, and therefore a large load is applied to the cylindrical inner peripheral surface of the bearing bush. The range of the cylindrical inner peripheral surface to which this large load is applied is approximately one-third of the entire circumference of the inner peripheral surface of the bearing bush.